Multiple FQDN for CIFS server

Currently in the process of moving an environment between two Active Directory domains. We have a NetApp controller running 9,0, serving CIFS file shares which we would like to cutover. Testing this we are having some trouble accessing the file shares from the old FQDN despite there being trusts setup and the DNS having A records created.

Server name: cifsserver

Old domain: domain.old

New Domain: domain.new

Accessing the CIFS server when joined to domain.new works ok using \\cifsserver, \\cifsserver.domain.new and \\<IP Address> using workstations from both domains. However trying to access the server using \\cifsserver.domain.old fails, despite there being a DNS entry and the server pingable using this address. There will be a few users who have mapped drives to the cifsserver.domain.old FQDN so we would like to get this working if possible.